1. Field of the Invention
This invention relates in general to apparatus for driving the components of a tape recorder; more particularly, the invention is concerned with apparatus for cooperating with a capstan drive assembly and for disposing magnetic tape around a recording drum so that a television signal train may be helically recorded on the tape. (As used herein, the term "recorder" shall be taken to mean apparatus which either, or both, records or plays back a video signal.).
2. Description Relative to the Prior Art
While it is not so restricted, the invention acquires a special significance when it is used with a video tape recorder of the type in which a magnetic tape is curved around a recording drum carrying one or more rotating heads. (Throughout, the terms "head" and "recording head" shall, obviously, mean a "playback head," as well.) The tape is wrapped so that it emerges from the drum at a different level from that at which it entered, describing a helical path as it travels around the drum. In this way, a television signal train may be provided to the heads and helically recorded on the tape. In existing reel-to-reel video recorders of this type, which take from one removable tape reel and pass it to another removable reel, the wrapping of the tape around the drum in preparation for recording or playback, and the unwrapping of the tape from the drum, are performed manually. Besides being an exacting and annoying operation, it may be difficult to optimally position the tape in is preferred helical path when the tape is manually wrapped around the drum.
With the introduction of video cassette machines, apparatus was devised for automatically threading the tape around the drum. In these machines, the tape is contained in a protective enclosure or cassette, and the entire enclosure is inserted into the machine. Generally, a tape door is automatically opened to allow one or more tape threading guides to be placed within the cassette and close to the tape. Without attempting to exhaustively list all the threading guide configurations that presently exist, there are a number of schemes for curving the tape around the drum which generally illustrate the state of the art. For instance, the threading guide may be mounted on a loading ring and driven counterclockwise in the loading operation and clockwise in the unthreading operation, e.g., U.S. Pat. No. 3,643,038. Most frequently, the loading ring is rim driven by a motor, which is correspondingly powered when the loading or unthreading function is selected. In another threading apparatus, a roller on the end of a pull-out arm, which operates in conjunction with the loading ring, withdraws the tape from the cassette, e.g., U.S. Pat. Nos. 3,784,761 and 3,821,805. Following withdrawal, the tape is transferred to the loading ring and wrapped around the drum.
Instead of providing a loading ring, other video cassette recorders use tape threading guides which move in paths defined by arcuate tracks on the deck of the recorder, e.g., U.S. Pat. No. 3,660,614. Motion is transmitted to the guides from a mechanical drive unit by means of a variety of mechanical linkages, levers, and gears. Arcuate tracks are avoided by U.S. Pat. No. 3,674,942, which discloses a pair of tape guides that slidably move in parallel tracks on either side of the recording drum. When mechanical linkages are used to move the threading guides, they may be designed to additionally move other components on the playing deck of the video recorder. For example, U.S. Pat. No. 3,673,348 discloses an erase head which is moved into contact with the tape by linkage with the same mechanism that advances the tape threading guides around the drum. The abovementioned U.S. Pat. No. 3,660,614 also provides a mechanical connection between a pinch roller and the guide advancing mechanism. As the guides wrap the tape around the drum, a mechanical linkage forces the pinch roller to resiliently engage the tape with a driving capstan.
What this prior art finally illustrates is that the basic challenge presented by helical wrapping is merely to move one or more tape threading guides around the recording drum and helically place the tape on the drum; the solution attempted should conceptually follow the most straightforward mechanical design to reach the intended result. Otherwise, some desirable feature or characteristic of the tape recorder may be needlessly sacrificed. Some approaches taken heretofore, as this brief overview of the prior art shows, use an elaborate network of linkages, levers, and gears to move the guides. As a result, cost is sacrificed in favor of complexity. When a less roundabout approach was attempted, as in the case of the loading ring, machine size was necessarily sacrificed.